Waveguide transition between rectangular and circular waveguides



Jan. 18, 1966 N. LIPETZ ETAL 3,230,484

WAVEGUIDE TRANSITION BETWEEN RECTANGULAR AND CIRCULAR WAVEGUIDES 2 Sheets-Sheet 1 Filed Oct. 22, 1963 INVENTORS, NATHAN LIPETZ CHARLES D. NEUDORFER Zf- W fig;

ATTORNEYS We H.441

Jan. 18, 1966 Filed Oct. 22

N. LIPETZ ETAL WAVEGUIDE TRANSITION BETWEEN RECTANGULAR AND CIRCULAR WAVEGUIDES 2 Sheets-Sheet 2 FIG, 3

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United States Patent The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to a rectangular to circular waveguide transition and more particularly to an end-feed type transition for circular waveguides propagating the TE mode.

It is well known that, for transmission over a considerable distance, the TE mode of propagation is that which involves the lowest attenuation loss. One method for establishing the TE mode in a circular waveguide is shown in Lanciani Patent No. 2,894,218 issued July 7, 1959. In this method, the circular waveguide is fed from a rectangular waveguide through four resonant slots or irises. The slots were radially mounted in the circular waveguide end plate and were slanted at an angle of 45 to the axis of the rectangular waveguide. It has been found that with the irises or slots so positioned, two components of the H-tfield can couple through the irises thereby creating a mode purity problem isasmuch as two possible axes of magnetic polarizabi-lity are involved. That is, the component perpendicular to the aris axis immediately creates a mode purity problem. While the use of a thick iris may alleviate this problem, the losses through the transition is increased. Furthermore, it was found that the Lanciani transition was effective only over a six percent bandwidth. Since a -12 percent bandwidth with good mode purity is required in many microwave systems, the use of the Lanciani transition is rather limited in such systems.

It is an object of the present invention to provide a rectangular to circular waveguide transition wherein the aforementioned limitations are overcome.

It is another object of the present invention to provide a relatively simple and compact apparatus for launching the TE mode in pure form in a circular waveguide.

It is still another object of the present invention to provide a coupling transition between a circular and rectangular waveguide which will have a wide bandwidth and a high degree of mode purity.

In accordance with the present invention there is pro vided a microwave transition for coupling the TE mode energy in a rectangular waveguide to a circular waveguide adapted to propagate the TE mode which includes means for dividing the power of the TE mode energy into two equal components and a waveguide chamber including two an'gularly disposed waveguide channels each having a pair of orthogonally positioned arms interconnected by a waveguide section one wall of which is common to both channels. Also included are discrete waveguide means coupling the respective power components to one arm of each of the waveguide channels with the portion of each of the waveguide coupling means proximal the arm being colinear with their associated arms. Included further is a waveguide matching section interconnecting the waveguide chamber and the circular waveguide, and an end plate separating the matching section and the waveguide chamber. The end plate includes a plurality of slots with a respective one of the slots being radially aligned with one of the orthogonally positioned arms of the waveguide channels. Alsoincluded are respective tuned shorting plates terminating the remaining arm in each of the waveguide channels.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is an exploded view illustrating the present invention;

FIG. 2 is a plan view of the waveguide chamber shown in FIG. 1 with the slotted end plate shown in phantom;

FIG. 3 is a cross section taken along the lines 33 of FIG. 2;

FIG. 4 is a cross section taken along the lines 4-4 of FIG. 1;

FIG. 5 is a cross section taken along the lines 5- -5 of FIG. 1; and

FIG. 6 is a curve illustrating the results obtained by the transition in accordance with the invention.

Referring now to FIGS. 1-3 of the drawing, there is shown at 10 a rectangular waveguide in which the TE mode is being propagated and which is coupled to circular waveguide 30 for propagating the TE mode by means of the transition 50. The transition 50 includes a Tchebysheif step transformer 52, an E-plane power splitter 54, a waveguide chamber section 56 terminated at one end by an end plate 58 provided with four slots or irises and at the other end by a solid plate 59, and a cruciform matching section 60. The longitudinal axis of the circular waveguide and co-axially arranged cruciform match ing section 60 is indicated at c. The waveguide chamber section 56 comprises two angular disposed waveguide channels 62 and 64 of identical construction and provided with a common septum or wall 66 with the longitudinal axis 0 of the circular guide 30 in the plane of septum 66. The surface of angular waveguide channel 62 opposite wall 66 is beveled as at 68 to so that the width of channel 62 is made uniform throughout. Similarly, the surface of angular waveguide channel 64 opposite common Wall 66 is beveled as at 70 so that the width of waveguide channel 64 is made uniform throughout. As shown, each of the channels 62 and 64 comprise two orthogonally positioned arms which are interconnected by the center wa veguide portion bounded by the beveled surface and the common septum. The arms of channel 62 are shown at 72 and 76 and the arms of channel 64 are shown at 74 and 78. The arms 72 and 74 are orthogonally arranged with respect to arms 76 and 7 8, with arms 72 and 76 of channel 62 being colinear with arms 74 and 78, respectively, of channel 64. The arms 72-78 thus may be said to comprise a cruciform arrangement. The depth or height of the waveguide channels 62 and 64 is along the axis c dimension. The width of both waveguide channels 62 and 64 are made equal. The channel arms 72-78 extend through the walls of waveguide chamber section 56 with the channel arms 74 and 76 being terminated by respective conducting end plates 80 and 82. The end plates 80 and 82 are so located within the respective channel arms 74 and 76 as to appropriately tune both the angular disposed waveguide channels to give optimum radio frequency matching between the waveguide channels 62 and 64 and the slot array of end plate 58 at the transition design center frequency. The orthogonally related open ended terminals of channel arms 72 and 78 are coupled to respective outputs of power splitter 54 by means of respective waveguides $4 and 86. The discrete outputs of power splitter 54 provide two equal power components of the TE mode propagated in input rectangular waveguide 10. As shown, the coupling waveguides 84 and 86 are arranged such that the discrete sections thereof, 83 and 85, proximal the channels 72 and 78 are axially aligned and colinear with their associated channels and thus provide two power output arms having a 90 angle therebet-ween. Of course, the coupling waveguides 84 and 86 are of equal length so that the both waveguide channels 62 and 64 are fed in-phase.

The waveguide channels 62 and 64 are coupled to matching section 60 by means of four slots or irises 88, 90, 92 and 94 in the end plate 58. The end plate 58 is so positioned that a respective slot is axially aligned with a discrete channel arm. Thus slots 88 and 90 are axially aligned with respective channel arms 74 and 78 of waveguide channel 64 and slots 92 and 94 are axially aligned with respective channel arms 72 and 76 of waveguide channel 62. In order for radial slots 88-94 to meet the requirements for TE mode propagation in circular waveguide 30, the following conditions must be satisfied. The slots 8894 should intercept the maximum E-field for the TE mode of waveguide channels 62 and 64. Also, the midpoints of the pair of slots 88 and 90 associated with waveguide channel 64, and the midpoints of the pair of slots 92 and 94 associated with waveguide channel 62, are spaced either a single one-half guide wavelength at the design center frequency of input rectangular waveguide 10 apart or an odd multiple of that half-guide wavelength apart. As indicated by the arrows e in FIG. 2, showing the electric vector in the E-plane, this half-wavelength spacing provides the necessary phase reversal and field orientation which are needed to establish the circular electrical field in the cylindrical waveguide 30. Each slot, or iris, transmits one-quarter of the waveguide input power. The width of the slots is made as large as possible consistent with low voltage standing wave ratio, maximum power handling capacity and mode purity. The length of the slots along the longitudinal axis of their associated channel arm is slightly less than one-half wavelength at the design center frequency of input rectangular waveguide 10.

The end shorting plates or plugs 80 and 82 which respectively tune the two channels 64 and 62 are also appropriately located with respect to the centers of respective slots 88 and 94. These shorting plates are spaced onequarter guide 10 wavelength or odd multiples thereof, preferably three-quarter guide wavelengths, from the center of their respective associated slot. Thus end shorting plate 80 will be spaced approximately three-quarter guide wavelengths from the center of slot 88 and shorting plate 82 will be spaced approximately three-quarter guide wavelength from the center of slot 94. As shown, the energy derived from slots 88-94 is coupled to circular waveguide 30 through a matching waveguide section 60. The matching waveguide section 60 comprises a true cruciform waveguide structure at the end proximal the slots 88-94 (FIG. 5), and a circular waveguide at the end connecting with circular waveguide 30 (FIG. 4). A gradual transition along the axis 0 from the cruciform waveguide structure to the circular waveguide is provided by gradually and uniformly reducing the depth of cruciform waveguide arms along the circular waveguide axis 0. The matching section 60 is positioned such that the respective waveguide arms of the cruciform are aligned with a respective one of the slots 88-94. Any suitable means such as the externally threaded bushing 100 adapted to engage both a threaded portion in transition section 50 provided therefor and locking rings 102 on matching section 60 may be utilized to maintain the cruciform matching waveguide section 60 in position over the slots 88-94.

It is well known that a plurality of identical slots spaced one-half guide wavelength along the edge of a waveguide section will each couple out an equal amount of energy. Since the power in input rectangular waveguide luis divided equally and in phase by power splitter 54 and then applied to respective angularly disposed waveguide channels 62 and 64, and because there are two slots in each waveguide channel spaced one-half guide wavelength apart, one-fourth of the total power in the original rectangular waveguide 10 will be coupled through each slot to its associated cruciform arm in matching section 60. Also, as mentioned hereabove, the odd multiple of halfguide wavelengths spacing between the two slots in each angularly disposed waveguide channel results in the necessary phase reversal in order to couple the energy of the two orthogonal TE modes in the cruciform matching section 69 which in turn supplies the TE mode energy to circular waveguide 30. Since the respective waveguides supplying the input to waveguide channels 62 and 64 are axially aligned with arm 72 of waveguide channel 62 and arm 78 of waveguide channel 64, and the slots 88 and 94 are respectively aligned with their associated waveguide channel anms, only one component of the H-field is coupled through the slots. The width and length of each slot also require a compromise between power handling capacity and mode purity. A slot width slightly less than one-quarter wavelength and a slot length slightly less than one-half wavelength has proven optimum. Field coupling through any slot to circular waveguide 30 through matching section 60 will tend to be parallel with the field of the TE mode in the circular guide 30. The curves of FIG. 6 illustrates the results obtained with the above described transition. The VSWR was less than 1.2:1 over the frequency range of 7 to 8 go. and the mode purity greater than 22 db. The bandwidth is in excess of 13%.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A microwave transition for coupling the TE mode energy in a rectangular waveguide to a circular waveguide adapted to propagate the TE mode comprising,

means for dividing the power of said TE mode energy into two equal components,

a waveguide chamber including two angularly disposed waveguide channels, each having a pair of orthogonally positioned arms interconnected by a waveguide section one wall of which is common to both of said channels,

discrete waveguide means coupling the respective power components to one arm of each of said waveguide channels, the portion of each of said waveguide means proximal said arms being colinear with each of their associated arms,

a waveguide matching section interconnecting said waveguide chamber and said circular waveguide,

an end plate separating said matching section and said chamber,

and a plurality of slots in said end plate, a respective one of said slots being radially aligned with one of said orthogonally positioned arms of said waveguide channels.

2. The microwave transition in accordance with claim 1 and further including a tuned shorting plate for each of the remaining arms of said waveguide channels.

3. The microwave transition in accordance with claim 1 and further including a transformer means leading from said rectangular waveguide to said power dividing means.

4. Waveguide apparatus for coupling the TE mode energy in a rectangular waveguide to the TE mode in a circular waveguide comprising,

a waveguide chamber including two angularly disposed rectangular waveguide channels, each having a pair of orthogonally positioned arms interconnected by a waveguide section one wall of which is common to both of said channels, the arms of said chambers being cruciformly arranged.

means for dividing the power of said TE mode energy into two equal components,

discrete waveguide means for respectively feeding said power components to one arm of each of said waveguide channels, the feeding ends of said waveguide means being orthogonally arranged and colinearly aligned with their associated waveguide channel arms, respectively,

a waveguide matching section interconnecting said waveguide chamber and said circular waveguide,

an end plate separating said matching section and said chamber,

four resonant slots cruciformly arranged in said end plate, a respective one of said slots being radially aligned with one of said orthogonally positioned arms of said waveguide channels, and with the center points of pairs of adjacent slots spaced an odd multiple half guide wavelength at the design center frequency of said rectangular Waveguide,

and respective tuned shorting plates terminating the remaining arms of said waveguide channels.

References Cited by the Examiner UNITED STATES PATENTS 2,800,632 7/1957 Walker 333-21 2,894,218 7/1959 Lanciani 3332l 2,954,558 9/1960 Honey et a1. 33321 HERMAN KARL SAALBACH, Primary Examiner.

G. TABAK, Assistant Examiner. 

1. A MICROWAVE TRANSITION FOR COUPLING THE TE10 MODE ENERGY IN A RECTANGULAR WAVEGUIDE TO A CIRCULAR WAVEGUIDE ADAPTED TO PROPAGATE THE TE01 MODE COMPRISING, MEANS FOR DIVIDING THE POWER OF SAID TE10 MODE ENERGY INTO TWO EQUAL COMPONENTS, A WAVEGUIDE CHAMBER INCLUDING TWO ANGULARLY DISPOSED WAVEGUIDE CHANNELS, EACH HAVING A PAIR OF ORTHOGONALLY POSITIONED ARMS INTERCONNECTED BY A WAVEGUIDE SECTION ONE WALL OF WHICH IS COMMON TO BOTH OF SAID CHANNELS, DISCRETE WAVEGUIDE MEANS COUPLING THE RESPECTIVE POWER COMPONENTS TO ONE ARM OF EACH OF SAID WAVEGUIDE CHANNELS, THE PORTION OF EACH OF SAID WAVEGUIDE MEANS PROXIMAL SAID ARMS BEING COLINEAR WITH EACH OF THEIR ASSOCIATED ARMS, A WAVEGUIDE MATCHING SECTION INTERCONNECTING SAID WAVEGUIDE CHAMBER AND SAID CIRCULAR WAVEGUIDE, AN END PLATE SEPARATING SAID MATCHING SECTION AND SAID CHAMBER, AND A PLURALITY OF SLOTS IN SAID END PLATE, A RESPECTIVE ONE OF SAID SLOTS BEING RADIALLY ALIGNED WITH ONE OF SAID ORTHOGONALLY POSITIONED ARMS OF SAID WAVEGUIDE CHANNELS. 